(1. 重庆理工大学 材料科学与工程学院，重庆 400050；
2. 重庆大学 材料科学与工程学院，重庆 400044)
摘 要: 为了优化镁合金棒材的微观组织，借鉴正挤压与多道次等通道挤压的特点提出了挤压(Extrusion)-剪切(Shear)复合挤压工艺(简称ES)，制造了多副适合工业卧式挤压机上的ES变形组合凹模，进行了ES挤压和普通挤压实验。构建了ES挤压和普通挤压的三维热力耦合的有限元模型及计算条件，模拟了ES挤压过程的挤压力、有效应力及应变演变规律，利用光学显微镜、透射及扫描电镜对微观组织演变进行了观察与分析。结果表明：根据对成形力演变过程和数值的分析，ES挤压过程可以分为四个阶段，其中有三个阶段挤压力变化较小，ES成形所需的挤压力大约是普通挤压所需挤压力的1.67倍；与普通挤压相比，ES挤压可大大提高镁合金的有效应变，最大有效应变可提高到3.8倍；ES成形可以改善镁合金中β相的形态与分布，不仅细化棒材表层晶粒，而且心部晶粒也得到了细化；动态再结晶晶粒及变形位错会越多，再结晶晶粒越细；带有转角的ES模具产生的剪切作用是镁合金发生多次动态再结晶的主要原因，在ES挤压过程中，第二相β相对基体有剪切和钉扎作用。
关键字: 变形镁合金；ES变形；微观组织；动态再结晶；应力状态
（1. College of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400050, China;
2. College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China）
Abstract:Based on the characteristics of direct extrusion and multi channels extrusion, the extrusion and shear (ES) was proposed to optimize the microstructures of magnesium alloy rods, and the ES deformation composite die suitable for industrial horizontal extrusion machine was manufactured. The ES extrusion and ordinary extrusion experiments have been carried out. The three dimensional finite element thermodynamic coupling model and conditions of ES extrusion and ordinary extrusion were established to simulate the evolution of extrusion pressure and cumulative stresses and strains during ES process. The microstructures evolution were studied by metallography, transmission and scanning electron microscopy. The results show that, according to the analysis about the values of forming forces, ES process can be divided into four stages, and three of which have little change of extrusion force. The extrusion forces of ES process is about 1.67 times that of ordinary direct extrusion. Compared with ordinary direct extrusion, ES process can greatly increase the cumulative strains of magnesium alloy, and the maximum strain is increased to 3.8 times. ES process can refine the alloy, improve the morphology and distribution of β phase and refine the grain sizes. ES process can refine not only the surface grains but also the center grains in the rods. The more the dynamic recrystallized grains and deformation dislocations, the finer the recrystallized grains. The main reason for multiple dynamic recrystallization of magnesium alloy is shear caused by ES die with shearing angles. During the process of ES deformation, the second β-phase has shearing and nailing action against the matrix alloy.
Key words: wrought magnesium alloy; ES deformation; microstructure; dynamic recrystallization; stress state
